1. Field of the Invention
The present invention is directed to a method used in the reconstruction of an image from computed tomography data to correct artifacts in the image arising due to overexposure of the radiation detector of the computed tomography apparatus.
2. Description of the Prior Art
The use of flat panel digital detectors for detecting x-ray radiation in computed tomography is becoming increasingly common. Typical flat panel digital detectors that are suitable for this type of use have a dynamic range of 14 bits. Digital image pixel processors that are conventionally used to process the raw image data reduce the dynamic range to only 12 bits, which is relatively small compared to the dynamic range of conventional computed tomography radiation detector, which typically is between 18 and 20 bits.
A dynamic range of 12 bits often is not large enough to avoid overexposure in the 2D projection images, namely the reconstructed density values (Hounsfield values) are too small. This negative impact is especially seen in 3D imaging. In addition, so-called “capping artifacts” arise. Capping artifacts occur because, even for a homogenous object, the reconstructed Hounsfield values are not reduced by a simple DC offset, but become increasingly smaller toward the edges of the object. This is schematically shown in FIG. 1 for a homogenous cylinder. Capping artifacts are very disturbing for detecting low contrast objects in the reconstructed images.